TC 9-64 _________________________________________________________________________
longitudinal waves, it is used in the study of both electromagnetic waves and
sound waves.
1-30. Consider the following example:
Two cycles of a wave pass a fixed point every second, and the velocity of the
wave train is 4 feet per second. What is the wavelength? The formula for
determining wavelength is as follows:
v
λ=
f
Where:
λ = wavelength in feet
velocity in feet per second
v=
f=
frequency in Hz
Given:
v = 4 feet per second
f = 2 Hz
Solution:
v
λ= f
4 feet per second
λ=
2 Hz
λ = 2 feet
1-31. In problems of this kind, be sure not to confuse wave velocity with
frequency. Frequency is the number of cycles per unit of time (Hz). Wave
velocity is the speed with which a wave train passes a fixed point.
1-32. Here is another problem:
If a wave has a velocity of 1,100 feet per second and a wavelength of 30
feet, what is the frequency of the wave?
By transposing the general equation:
v
f=
λ
We have the equation:
v
λ=
f
Given:
v = 1,100 feet per second
λ = 30 feet
Solution:
1,100 feet per second
f=
30 feet
f=
36.67 Hz
To find the velocity, rewrite the equation as follows:
v = λf
1-10
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